JP5589056B2 - Contact element for conductively connecting the anode and interconnector of a high temperature fuel cell - Google Patents

Description

  The present invention relates to a contact element that conductively connects an anode and an interconnector of a high-temperature fuel cell. In a high-temperature fuel cell, individual fuel cells are combined to form a stack, in which case they are always electrically connected to each other. For this purpose, an interconnector, also called a bipolar plate, is arranged between the electrodes of the individual fuel cells. Therefore, a current can flow from one electrode of a certain fuel cell to the opposite electrode of the adjacent fuel cell.

  However, since it is necessary to move the fuel or oxidant to the electrode, it must be permeable or porous, which affects conductivity.

  Therefore, so far, various configurations of current connectors have been used between the electrodes and the respective interconnectors. An example of this is a network or current connector made of fiber (German Patent Application No. 10232093 (A1)).

  In the case of a high-temperature fuel cell, since the operating temperature of the fuel cell is high, the further problem of thermal expansion must generally be considered. For this reason, the coefficient of thermal expansion of the solid electrolyte is usually taken into account when selecting the materials of all the individual essential elements of the fuel cell, i.e. the electrode and interconnector material, and in part the current connector material. To do. In this case, only slight differences should be allowed.

  Current connectors that provide a conductive connection between the anode and the associated interconnector are typically made of nickel. However, nickel has a considerably high coefficient of thermal expansion. When the high temperature fuel cell is cooled from the operating temperature to room temperature, the length in contact with the anode is insufficient. This can cause tensile strain on the ceramic contact of the cathode, which can break the contact. This causes electrical losses and reduces the power that can be achieved.

  This reduction in the thickness of the conductive connection formed of nickel between the anode and the interconnector is also not appropriate because the mechanical strain and manufacturing tolerances must be compensated for by the ductility of nickel.

  In forming a contact using a mesh or fiber structure between the anode and the interconnector, a spot having increased conductivity due to local deformation during the operation of the fuel cell, a so-called “hot spot” Is generated. More current flows through that part.

  In this process, if contact at these locations is hindered, inevitably the conductivity decreases and the electrical resistance increases. This means that there is no such contact in such a current connector, at least in such a time that a limited amount of current can flow locally between the anode and the interconnector, so the power is turned off. It has a particularly detrimental effect on restarting conventional fuel cells.

German Patent Application No. 10232093 (A1)

  Accordingly, it is an object of the present invention to achieve a stable, more reliable conductive connection over a long period of time between the anode of a high temperature fuel cell and its associated interconnector.

  According to the invention, this object is achieved by a contact element having the features of claim 1. Advantageous embodiments and further developments of the invention can be achieved with the technical features described in the dependent claims.

  The contact element according to the invention is formed by a conductive subelement consisting of two regions. In this regard, one subelement contacts the anode and the other subelement contacts each interconnector. The contact elements are permeable because the partial elements form holes through which fuel can pass through the contact elements. Both subelements are formed of materials having different coefficients of thermal expansion.

  The subelements and the contact elements as a whole are also porous.

  The contact element may be formed of more than two subelements. In this process as well, the coefficient of thermal expansion is considered.

  Due to the different coefficients of thermal expansion, deformation occurs when the temperature changes. By causing compressive strain in the contact element, the conductive contact can be stabilized. The compressive strain occurs in a distributed manner on the surface of the contact element. This allows current to flow in more distributed locations on the effective surface between the anode and interconnector.

  When deformed, peaks and troughs can be distributed on the surface of the contact element. In this regard, the trough is preferably at the hole. Although the contact element is deformed when cooled from the operating temperature of the high temperature fuel cell, it can be used to create a region pushed to the anode side and a region pushed to the interconnect side. Thereby, electrical contact can be improved.

  This effect can be used for all further temperature changes.

  The coefficients of thermal expansion of the materials forming the two subelements should be separated so that the difference in expansion is at least 1 ppm / K. This should be maintained at a temperature range of at least 700 ° C. to the operating temperature of the high temperature fuel cell.

  The holes formed in the subelement should be arranged so that the contact element is permeable to the fuel and that each hole in one subelement communicates with each hole in the other subelement.

  When selecting sub-element materials and determining their dimensions, the size of the two sub-elements should be equal or equivalent at a temperature of at least 100K below the operating temperature of the high temperature fuel cell. Can be considered.

  When determining the shape and size of the surface of the sub-element, it is advantageous that the outer edge element formed in the periphery contacts the outer edge of the sub-element at a temperature of at least 100 K, which is less than the operating temperature of the high temperature fuel cell. Can be determined. However, this state may already be achieved at room temperature.

  However, the outer edges of the subelements of the contact element may be secured to the outer edge elements alone or in advance around the perimeter and / or the subelements may be connected to each other at their outer edges. It may be.

  Deformations that can be advantageously used in the present invention can be performed on the surface of the contact element during these temperature changes by these methods.

  The contact element according to the invention should be flexible and permeable to gases. For this purpose, the partial elements can be made of a transparent film that can be deformed flexibly.

  In this regard, each subelement can be formed of a different metal selected from nickel, copper, iron, cobalt, or an alloy thereof.

  The total thickness of the contact element should be at most 2 mm.

  The thickness of the two partial elements of the contact element according to the invention may be different. In this regard, the respective coefficient of thermal expansion, mechanical properties (eg, flexibility), and respective conductivity can be considered.

  Sub-element holes should be 20% to 90%, preferably 40% to 60% of the anode and / or interconnector surfaces to ensure that sufficient fuel changes can be made to maintain high conductivity.

  The holes should be regularly and evenly spaced from each other and their dimensions and shapes should be equivalent, but this should apply at least in the central region. The holes may be arbitrarily different at the outer edge, or no holes may be provided.

  A partial element having a high coefficient of thermal expansion should be arranged on the side of the contact element facing the anode, and a partial element having a low coefficient of thermal expansion should be arranged on the side of the contact element facing the interconnector.

  The following examples explain the invention in more detail.

1 is a cross-sectional view of a high temperature fuel cell with a contact element according to the present invention. FIG. 4 shows a partial element of an example of a contact element according to the invention.

  A cross-sectional view of the high-temperature fuel cell is shown in FIG. In this regard, a contact element 1 is arranged on the interconnector 3 between the interconnector and the anode 2. A solid electrolyte 4 and a cathode 5 are disposed on the anode 2.

In this example, the two partial elements 1.1 and 1.2 form the contact element 1. In this regard, the partial element 1.1 arranged on the interconnector side is made of pure copper (α = 16.5 * 10 ⁻³ K ⁻¹ at 20 ° C.) and has a thickness of 290 μm. The second partial element 1.2 arranged on the anode side is formed of a thin film of pure nickel (α = 13.0 * 10 ⁻³ K ⁻¹ at 20 ° C.) having a thickness of 120 μm.

1 Contact Element 1.1, 1.2 Partial Element 2 Anode 3 Interconnector 4 Solid Electrolyte 5 Cathode

Claims (12)

A contact element disposed between the anode and the interconnector for conductively connecting the anode and the interconnector of the high-temperature fuel cell,
The contact element is formed of a conductive sub-element comprising two regions, one sub-element is in contact with the anode, the other sub-element is in contact with the interconnector;
Hole is formed on each of the other part element and the one of the partial elements,
Forming the one partial element and the other partial element with materials having different coefficients of thermal expansion;
Contact element characterized by. The hole formed in the one partial element and the hole formed in the other partial element are arranged so that the contact element is permeable to fuel. Contact element. The contact element according to claim 1, wherein the one partial element and the other partial element have the same size at a temperature that is at least 100 K lower than an operating temperature of the high-temperature fuel cell. . In at least 100K lower temperature than the operating temperature of the high temperature fuel cell, the outer edge of the outer edge and the other partial element of the one part element, and wherein, be in contact with the outer edge elements formed around The contact element according to any one of claims 1 to 3. The periphery of the outer edge of the one partial element of the contact element and the periphery of the outer edge of the other partial element are fixed to the outer edge element, and / or the one partial element and the other partial element The contact elements according to claim 4 , characterized in that they are interconnected at least at their outer edges.   The contact element according to claim 1, wherein the contact element is flexibly deformable. The contact element according to any one of claims 1 to 6, wherein the one partial element and the other partial element are perforated films that can be flexibly deformed. The one partial element and the other partial element are formed of a metal selected from nickel, copper, iron, and cobalt, or an alloy of these metals, according to any one of claims 1 to 7. The described contact element.   The contact element according to claim 1, wherein the one partial element and the other partial element have different thicknesses. The hole of the hole and the other part element of the one part element, occupy 90% to 20% of the surface and / or the interconnector surface of the anode, from claim 1, wherein the 9 Contact element according to any one of the preceding claims. Contact element according to claim 1, any one of 10 the holes are arranged so as to be regularly and equidistantly to each other, that dimensions and shape of the holes is equal, and wherein.   The one partial element arranged on the anode side has a thermal expansion coefficient larger than that of the other partial element arranged on the side facing the interconnector. Contact element according to paragraph.

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